Wave Asymmetry Research Articles

Lagrangian description of gravity-capillary waves propagating on a sloping bottom

An asymptotic solution that describes a small amplitude gravity-capillary wave propagating on the surface of a gentle sloping beach is derived in the Lagrangian coordinates. The analytical solution in Lagrangian form satisfies the zero pressure at the free surface. In the Lagrangian approximation, the parametric expression of water particles can be obtained directly and explicitly as a function of the wave steepness, the bottom slope and surface tension. The analytical solution for wave asymmetry parameter up to the breaker line for an arbitrary bottom slope can also be derived. The Lagrangian solution enables the description of the features of wave shoaling in the direction of wave propagation from deep to shallow water, as well as the process of successive deformation of a wave profile which leads to wave breaking. Furthermore, by comparing the theoretical values of wave asymmetry with experimental results, it is found that theoretical results of the present solution are in good agreement with the experimental data. It is also found that surface tension lower the breaking wave height, lengthen the wave length and increase the breaking water depth.

The seabed boundary layer beneath waves opposing and following a current

The effect of streaming on the sea bed boundary layer flow beneath combined waves and current has been investigated for waves following and opposing a current, taking both linear waves and second order Stokes waves into account. This flow results from an interaction between the classical wave–current seabed boundary layer mechanism and two different streaming mechanisms. The classical wave–current seabed boundary layer mechanism leads to a reduced mean velocity relative to the current alone; the two streaming mechanisms are streaming caused by turbulence asymmetry in successive wave half-cycles (beneath asymmetric forcing) and streaming caused by the presence of a vertical wave velocity within the seabed boundary layer as earlier explained by Longuet-Higgins. The effect of wave asymmetry, wave length to water depth ratio, magnitude of current and bottom roughness have been investigated by numerical simulations for realistic physical situations. Mean Eulerian quantities as well as the mass transport (wave-averaged Lagrangian velocity) are presented. The resulting sediment dynamics near the ocean bottom has been investigated; results for both suspended load and bedload are presented. For wave dominated situations, the velocity profiles beneath opposing waves and current are substantially different from those beneath following waves and current, both for linear and second order Stokes waves. As the flow becomes current dominated, the velocity profiles beneath opposing and following waves and current approach the velocity profile beneath horizontally uniform sinusoidal forcing. The net transport of suspended sediments and bedload is in the direction of the current both for waves following and opposing the current. For wave dominated situations the net sediment transport is strongly affected by the streaming mechanisms, both for linear and second order Stokes waves and current.

Characterization of storm wave asymmetries with functional data analysis

Functional data analysis (FDA) is a set of tools developed to perform statistical analysis on data having a functional form. In our case we consider the one-dimensional wave surface profiles registered during a North-Sea storm as functional data. The data is split into 20 min intervals within which an individual wave is defined as the profile between two consecutive downcrossings. After registration of these individual waves to the interval [0, 1], the mean wave profile for the entire 20 min interval is obtained along with the first two derivatives of this mean profile. We analyze the shape of these mean waves and their derivatives and show how they change as a function of the significant wave height, which is a measure of the severity of the sea for the corresponding time interval. We also look at the evolution of the energy, as represented by the phase diagram, as a function of significant wave height. The results show the asymmetry in vertical and horizontal scales for real data. Comparison with a Gaussian wave simulation model calculated from the actual wave spectra shows important differences in symmetry and shape of the average wave and seem to indicate that the greatest difference in the distribution of energy during the wave cycle lies in the second and fourth quarters of the wave period. FDA can be applied to derive information on the individual and average wave profiles and also provide an understanding of the variation in energy throughout the wave phase.

A Novel Method of Predicting Aortic Valve Opening through LVAD Power Waveform Analysis

Purpose Aortic valve opening (AVO) during left ventricular assist device (LVAD) support has important clinical implications in preventing thrombosis and leaflet fusion causing chronic regurgitation. Assessment of AVO has become part of routine LVAD care. Traditionally, this has been done with transthoracic echocardiography (TTE) but that technology is costly and not always readily available, especially as patients are increasingly released back to their communities. This study investigates the use of LVAD power waveform analysis as a faster and inexpensive method of evaluating AVO in LVAD patients. Methods and Materials Waveforms were collected from HeartMate II LVAD controllers and saved in The Artificial Heart Program database. Waveforms were then matched with corresponding TTE reports to determine AV status. A LabView program was used to filter and analyze these power waveforms and output characteristics of each wave. These characteristics were then stratified into AV opened or AV closed groups. Averages of parameters for each group were taken and compared using a two-tailed Student’s t-test. Results 492 AV closed waveforms were obtained from 39 patients and 168 AV opened waveforms were obtained from 19 patients. Patients with open AV are shown to have higher average wave amplitudes, and took a larger percentage of time to reach max amplitude as shown by the skewness which is a measure of wave asymmetry. Conclusions We describe an innovative and inexpensive method of detecting significant differences between open and closed AV. Further study is needed to create and validate a user interface in LabView to input an unknown waveform and be able to predict AVO within a reliable accuracy level. AV Closed (n=492) AV Open (n=168) Waveform Characteristics μ ± μ ± p-values Baseline Current (mA) 303 77 305 83 0.85 Amplitude (mA) 139 37 160 50 Skewness 0.07 0.41 -0.08 0.44 Table 1 μ: mean, ±: standard deviation

경사면을 입사하는 불규칙파랑의 방향 비대칭 매개변수 및 최대 방향분포 매개변수

해안선에 비스듬히 입사하는 다방향 불규칙파랑은 굴절에 의해 방향 비대칭성이 발생한다. 방향 비대칭은 최대 방향분포 매개변수(S max )와 연관된 비대칭 매개변수의 항으로 표현된다. 본 연구에서는 심해에서 다양한 주파향각과 최대 방향분포 매개변수 등의 특징을 갖는 다방향 불규칙파랑에 대해 수심 변화에 따른 비대칭 매개변수와 최대 방향분포 매개변수의 변화를 계산하였다. 계산 값들은 파랑의 방항 비대칭성을 무시한 Goda and Suzuki(1975)에 의한 결과와는 다르다. 비대칭 매개변수와 최대 방향분포 매개변수의 계산을 위해 JONSWAP 스펙트럼(Hasselmamn et al., 1973)과 Lee et al.(2010)의 방향 분포 함수를 사용하였다. 계산 과정과 결과들은 일반화를 위해 심해에서의 유의파고, 첨두주기, 첨두주기에 해당하는 파장 등으로 무차원화 하였다.

뇌파유형별 향기에 따른 인체의 심리적 및 생리적 차이 비교

본 논문에서는 3가지 향기가 뇌파유형에 따른 피험자에게 미치는 영향과 피험자의 쾌적성 및 생산성을 향상시킬 수 있는 최적의 향기를 찾기 위한 연구를 하였다. 피험자들을 A타입과 B타입으로 분류하여 뇌파(EEG), 학습능력 및 심박동변이(HRV)를 측정하여 쾌적성, 집중력, 스트레스 및 심장박동의 변화를 분석하였다. 항...

Effect of asymmetry of incident wave on the maximum runup height

Didenkulova, I., Denissenko, P., Rodin, A. and Pelinovsky, E., 2013. Effect of asymmetry of incident wave on the maximum runup height.Shoaling and runup of long waves on a beach form a classical task for coastal oceanography and engineering. Though many empirical and theoretical formulae have been developed in this field, most of them are targeted to typical waves and situations, while the greatest hazard is caused by extreme events, such as, for example, extreme storms and catastrophic tsunamis. From this point of view it was shown theoretically that one of the most important parameters which influence the wave runup height is the steepness of the incident wave front and the asymmetry of the incident wave. It helped to provide a simple explanation to the extreme runup observed during the catastrophic 2004 Indonesian tsunami event. However, the theoretical results were obtained under many assumptions (ideal fluid, no wave breaking, no bottom friction) and have not been validated. Here we present an experimental study performed in the Large Wave Flume (GWK), Hannover, Germany, which is focused on the influence of the asymmetry caused by the non-linear deformation of incident waves on their runup on a plane beach. The series of experiments are aimed to validate the theoretical formulae for runup height of asymmetric waves. Obtained results are in a good agreement with theoretical predictions and corresponding formulae are recommended to be considered in wave forecasts.

On the Predictability of Mid-term Cross-shore Profile Evolution

Fernàndez-Mora, À., Calvete, D., Falqués, A., Ribas, F., and Idier, D., 2013. On the Predictability of Mid-term Cross-shore Profile EvolutionThe aim of the present study is to analyse the mid-term beach profile evolution, considering the hypothesis that the alongshore processes can be neglected for the prediction of the mean profile evolution. To this end, a process-based model for the evolution of the cross-shore profile has been used. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, accounting for the effects of wave skewness and asymmetry on sediment transport. Offshore waves and tides conditions and bathymetric profiles measured at the FRF-USACE Duck are used to simulate a mid-term (72 days) onshore sandbar migration event. The model results agree with observed onshore movement and growth of the sandbar due to the inclusion of the intra-wave oscillatory flow with the skewness and asymmetry effects. The best predictions belongs to the averaging of the modelled evolution of individual cross-shore profiles that is better than the evolution of the mean cross-shore profile since. it takes into account the alongshore variability of the cross-shore profiles. These two methods result on better predictions than the individual profiles during the entire event.

MATERIAL PLACEMENT IN THE NEARSHORE: LABORATORY AND NUMERICAL MODEL INVESTIGATION

Typical practice for a century has been to transport dredged sand to an offshore disposal site in deep water where the sediment is lost from the littoral system. The alternative of nearshore placement can retain the sand, but the fate of the material is poorly understood. A set of laboratory experiments were conducted, using tracer sand, with the intent of quantifying the migration of material with alternative dredged mound placements within the surf zone. Conventional depth-integrated tracer sand transport models can utilize a correction factor or a gradient diffusion mechanism to represent the effects of the depth variation. In the surf zone, however, an analytical correction factor is not available and a gradient diffusion coefficient is arbitrary with no physical basis. An alternative simple advective transport sand model is introduced herein that explicitly predicts both the advection associated with the return current and the wave-related onshore transport. With a simple
 framework based on a suspended layer and a bedload layer of arbitrary transport directions, the Taylor dispersion of tracer sand is explicitly computed without any dependence on a diffusion mechanism. Both the modeled and measured results indicate transport directed offshore by the undertow, onshore by the wave asymmetry, and down-drift as forced by the longshore current.

A MULTIPLE-SIZED TRANSPORT FORMULA FOR NONUNIFORM SEDIMENTS UNDER CURRENT AND WAVES

Nonuniform sediment transport exhibits difference from uniform sediment, even when the mean grain size is the same for both cases. The hiding, exposure, and armoring among different size fractions in the nonuniform bed material may significantly affect sediment transport, morphological change, bed roughness, wave dissipation, etc. It is necessary to develop multiple-sized sediment transport capacity formula to improve the accuracy and reliability of coastal analysis tools. The Wu et al. (2000) formula, which was developed for river sedimentation, is herein extended to calculate multiple-sized sediment transport under current and waves for coastal applications. This formula relates bed-load transport to the grain shear stress and suspended-load transport to the energy of the flow system. It considers the effect of bed material size composition in the hiding and exposure correction factor, which is omitted in many other existing formulas. Methods have been developed in this study to determine the bed shear stress due to waves only and combined current and waves, and in turn to compute the bed-load and suspended-load transport rates using the Wu et al. (2000) formula without changing its original formulation. The enhanced bed-load formula considers the effect of wave asymmetry on sediment transport, calculates the onshore and offshore bed-load transport rates separately and then derives the net transport rate, whereas the enhanced suspended-load formula calculates only the net transport rate due to the limit of available data. The formula has been tested using the single-sized and multiple-sized sediment transport data sets. The formula provides reliable predictions in both fractional and total transport rates. More than half of the test cases are predicted within a factor of 2 of the measured values, and more than 90% of the cases are within a factor of 5. This accuracy is generally reasonable for sediment transport under current and waves, which is very complex and little understood.

Nonlinear Effects in Gravity Waves Propagating in Shallow Water

Nonlinear energy transfers due to triad interactions change the characteristics of the wave-field in the shoaling region. The degree of nonlinear coupling is examined using numerical simulations based on an accurate set of deterministic evolution equations for the propagation of fully dispersive weakly nonlinear waves. The model validation, using existing experimental measurements for wave transformation over a shoal, showed that it accurately predicts nonlinear energy transfer for irregular waves with large wave-numbers. The bound higher harmonics and nonlinear statistical measures, i.e. the wave skewness and asymmetry, are well simulated by the model in both the shoaling and deshoaling regions. Numerical simulation of steep waves in shallow water with the Ursell number O(1), showed that nonlinear dispersion and phase locking lead to triad interactions even on a horizontal bottom. Nonlinear energy transfers in monochromatic waves lead to rapid spatial recurrence of the primary wave amplitudes. This is in contrast to the case of irregular waves where the Fourier coefficients of the wave-field do not recur due to the presence of innumerable interactions, which are expected to cancel resulting in no spatial evolution of the wave spectrum.

Transient Evolution of Langmuir Turbulence in Ocean Boundary Layers Driven by Hurricane Winds and Waves

Abstract A large-eddy simulation (LES) model, which adopts wave-averaged equations with vortex force, is used to investigate Langmuir turbulence and ocean boundary layer (OBL) dynamics in high-wind hurricane conditions. The temporally evolving spatially asymmetric wind and wave Stokes drift velocity imposed in the LES are generated by a spectral wave prediction model adapted to Hurricane Frances traveling at a speed of 5.5 m s−1. The potency of Langmuir turbulence depends on the turbulent Langmuir number, the wind–Stokes drift alignment, and the depth scale of the Stokes profile Ds relative to the OBL depth h. At the time of maximum winds, large-scale vigorous coherent cells develop on the right-hand side of the storm under the inertially rotating winds; the Stokes drift velocity is well tuned to the surface winds. Much weaker cells develop on the left-hand side of the storm, partly because of reduced Stokes production. With misaligned winds and waves the vertical momentum fluxes can be counter to the gradient of Stokes drift, and the cell orientation tracks the direction of the mean Lagrangian shear. The entrainment flux is increased by 20% and the sea surface temperature is 0.25 K cooler on the right-hand side of the storm in the presence of Langmuir turbulence. Wave effects impact entrainment when the ratio Ds/|h| > 0.75. Because of wind–wave asymmetry Langmuir cells add quantitatively to the left–right asymmetry already understood for hurricanes due to resonance. And the transient evolution of the OBL cannot be understood simply in terms of equilibrium snapshots.

조도 변화에 따른 뇌파 기반 생체신호 변화에 관한 연구

By using EEG and HRV, subjects were estimated on their psychological and physiological reaction when reading psychrometric chart in 7 point century font, in an environmental test room in the condition of temperature 25[℃], relative humidity 50[RH%] , air current speed 0.02[m/sec], giving variation in illuminance to 0.1, 300, 600, 1000, 1300 and 1600[lux]. As a result, it was at 1300[lux] that absolute α wave, SMR, SDNN were most vitalized, and also both sides α wave asymmetry index, SEF50, HRT, stress and fatigue degree were at the lowest. It was found that a certain illuminance which minimizes psychological stress and fatigue degree while enhancing concentration and task achievement stably does exist. <BR>

Reversed sediment wave migration in the Irish Sea, NW Europe: A reappraisal of the validity of geometry-based predictive modelling and assumptions

The observation and prediction of the mobility of the seabed are in high demand with rapidly expanding offshore engineering developments and the increasing urgency to start mitigation against changing coastlines. From repeatedly surveyed sediment wave fields in the Irish Sea, average sediment wave migrations have been mapped, from which broad-scale net sediment transport directions can be derived. The proximity of bathymetric highs and lows seems to redirect sediment migration pathways and increases migration rates by a factor 5 on average via current deflection and amplification. A few hundred sediment waves were analysed geometrically in this study and compared to their migration behaviour, revealing a lack of statistical correlation. Sediment wave lee slope directions, asymmetry indices and other geometrical parameters appear poorly indicative of their degree of mobility in the Irish Sea. A considerable amount of sediment waves counter-intuitively migrate in the direction of their gentle stoss slope, i.e. opposite to the expected sense of migration. Even when considering the limitations of the predominantly 2-dimensional sampling method, these results fundamentally challenge established assumptions on the indicative meaning of sediment wave geometry. They question the validity and robustness of sediment wave migratory predictions based on single geometrical readings that fail to represent the complexity of local hydrodynamics and partial sediment wave modifications. Until predictive tools for sediment wave migration are developed that can pass the test in all aquatic environments, repeat surveying with sonar systems provides the only reliable way to record true natural variability.

Calculation of Solitary Wave Shoaling on Plane Beaches by Extended Boussinesq Equations

In this study, shoaling phenomenon is analyzed using Galerkin finite element approach. This numerical scheme is applied to the extended Boussinesq equations derived by Beji and Nadaoka (1996) for simulation of shoaling on plane beaches. For spatial discretization, quadratic elements with three-station Lagrange interpolation polynomials are used for horizontal velocity and the water surface elevation. However, for time discretization, two different numerical schemes are used. The first method is a combination of semi-implicit schemes with low-order backward finite difference for time integration and the second method is high-order AdamBashforth-Moulton predictor-corrector strategy. Based on this numerical approach, shoaling phenomenon caused by propagation of a solitary wave on sloped beaches is modeled and the results are compared with the available results from the fully nonlinear potential flow model. Considering the fact that the extended Boussinesq equations are affected by nonlinear effects, a non-dimensional parameter called “Asymmetric Parameter” is introduced. This parameter expresses the effects of the travelled distance of the solitary wave as well as the relative wave height on the resulting wave asymmetry. Finally, using this parameter, shoaling coefficient has been computed in an appropriate range.

Measurements of wave-induced steady currents outside the surf zone

Experimental measurements of the steady current induced by progressive regular waves outside the surf zone are reported and discussed herein. The experiments have been conducted in a large wave flume to minimize scale effects. The velocity data were acquired using Acoustic Doppler Velocimeters. It has been observed that the mean velocity profiles have a pronounced dependence on the wave period. As it decreases, the mean velocity just below the wave trough increases in the offshore direction while close to the bottom it increases in the onshore direction. The observed qualitative trend is different from that predicted by the theory and also from that reported by other experimental campaigns. The presence of turbulence in the bottom boundary layer along with wave asymmetry partially explain these differences. However, other experimental data in the literature agree with the present results.

Addendum au supplément 2, volume 59 (2011), de la Revue d’épidémiologie et de santé publique : « XXIV e Congrès national Émois (Nancy, 17–18 mars 2011) »

A new mathematical derivation is developed to describe the periodic gravity surface waves propagating on sloping bottoms. In the Eulerian coordinate system, the velocity potential is obtained as a function of the wave steepness ɛ to the first order and the bottom slope α to the third order. The wave profile is then transformed into the Lagrangian system, and the analytical solution of wave profile and asymmetry parameter on a given bottom can thus be obtained. These enable the description of the features of wave shoaling in the direction of wave propagation from deep to shallow water, particularly, the process of successive deformation of a wave profile. Furthermore, by comparing the theoretical values of wave asymmetry with experimental data, it is found that theoretical results of the present solution has similar tendency with the experimental data.

Stochastic Asymmetry Properties of 3D Gauss-Lagrange Ocean Waves with Directional Spreading

In the stochastic Lagrange model for ocean waves the vertical and horizontal location of surface water particles are modeled as correlated Gaussian processes. In this article we investigate the statistical properties of wave characteristics related to wave asymmetry in the 3D Lagrange model. We present a modification of the original Lagrange model that can produce front-back asymmetry both of the space waves, i.e. observation of the sea surface at a fixed time, and of the time waves, observed at a fixed measuring station. The results, which are based on a multivariate form of Rice's formula for the expected number of level crossings, are given in the form of the cumulative distribution functions for the slopes observed either by asynchronous sampling in space, or at synchronous sampling at upcrossings and down-crossings, respectively, of a specified fixed level. The theory is illustrated in a numerical section, showing how the degree of wave asymmetry depends on the directional spectral spreading and on the mean wave direction. It is seen that the asymmetry is more accentuated for high waves, a fact that may be of importance in safety analysis of capsizing risk.

Study of “Wave Type” Uneven Settlement and Reinforcing Method of Soft Clay Foundation

The deformation is the dominant factor of the quality of the road constructed on the soft soil foundation. Tianjin DongJiang port is located on the hydraulic filled soil foundation which is improved by using vacuum preloading method. Roads in this area often suffer wave type asymmetry settlement, which serious affects the usage of the road and causes damage to both vehicles and human being. It is found that the initial wave asymmetry deformation of the road on very soft soil foundation usually exists and will be developing continuously under the traffic load. The mechanism of the wavy failure of the road is discussed by establishing a mechanical model. The method of using geogrids to reduce the asymmetry deformation is proposed, the reinforce effect is analyzed using finite element method.

Sediment transport associated with morphological beach changes forced by irregular asymmetric, skewed waves

[1] The waveshape effects on sediment transport are investigated for cross-shore beach profile changes. This study is based on experiments performed in the Laboratoire des Ecoulements Geophysiques et Industriels wave flume for irregular waves. The interest of such experiments resides in presenting complex combinations of wave skewness and asymmetry in bed load, ripple, and sheet flow regimes. Net sediment transport rates on typical beach morphodynamics are analyzed in regard to wave skewness and asymmetry, undertow, and ripple occurrence. Onshore bar migration is mainly associated with onshore-directed sediment transport, whereas terrace profile and offshore bar formation correspond to offshore sediment transport. As for natural beaches, energetic (moderate) wave climates mostly induce offshore (onshore) sediment fluxes. For a given significant wave height, an increase (decrease) in the wave climate peak period is associated with an increase (decrease) in wave skewness and leads mostly to offshore (onshore) sediment fluxes. The experiments are fully characterized by unsteady behavior. Consequently, several conditions exhibit phase-lag effects where the sediment is mobilized by the wave crest and transported by the following trough, which produces a net offshore transport even for a weak undertow. The presence of ripples clearly contributes to enhance this behavior. An original concept, due to its application to skewed asymmetric irregular waves, presents the important interaction between wave nonlinearities driving the sediment fluxes. The net sediment transport rate under strongly skewed waves is either offshore directed due to phase-lag effects or onshore directed when the wave asymmetry is large enough. Both these mechanisms probably largely contribute to bar formation and migration.